Chromium complex dyes are widely known as a class of materials useful as charge control agents in dry toner corresponding to this invention. U.S. Pat. No. 4,401,741 to Miyakawa is illustrative. Commercial suppliers offer various chromium complex dyes explicitly for use as such charge control agents, but none are known to be so offered which are closely similar to either of the dyes used together in accordance with this invention.
The Material Safety Data Sheet for the IBM 3812 and 3816 toners includes a dye as the apparent charge control agent as follows: Azoid dye, CAS No. 41741-86-0. BASF offers commercially a dye with this CAS No. 41741-86-0. It is called Zapon Yellow 156. (Zapon is a registered trademark.) The Material Safety Data Sheet for Zapon Yellow 156 states that both Solvent Yellow 21 and C.I. 18690 are synonyms to Zapon Yellow 156. The Colour Index gives the following description of C.I. 18690: A chromium complex of ##STR1## Anthranilic acid-&gt;3-methyl-1-phenyl-5-pyrazolone, (meaning the acid is first diazotized and then coupled with the pyrazolone).
Nevertheless, attempted use of Zapon Yellow 156 in toners formulated otherwise in accordance with this invention was not successful.
This invention employs a mixture of Solvent Yellow 81 dye and Solvent Orange 56 dye, sold as Zapon Yellow 141. The following two references are known only from database summaries in English. The first mentions Solvent Yellow 81 and the other mentions Solvent Orange 56 as dyes in toner, but not as general purpose charge control agents and not in combination: Japanese patent JP3094270-A issued Apr. 19, 1991, to Ricoh K. K. and Japanese patent J62024268-A issued Feb. 2, 1987, to Ricoh K. K.